The present invention relates to a method of printing an apparently continuous stripe of constant width and straight edges, and more particularly to a method for printing the same using a movable flat-bed table-top image-impressing devices such as a silk screen.
For the purposes of the following specification and claims, the short stripe (or longitudinal section of a longer stripe) laid down by an image-impressing device in a single position is referred to as a "minor" stripe, and the full-length stripe comprised of a plurality of minor stripes in generally longitudinally alignment is referred to as a "major" stripe.
A preferred method of printing a stripe on an elongated substrate, such as a length of wallpaper or textile goods, is to lay a length of the substrate out on the top of a long table and then move a movable flat-bed image-impressing device, such as a silk screen, over the substrate length. The image-impressing device is first placed on one length of the substrate and then, after the stripe-defining image is impressed, raised and lowered onto a successive length of the substrate, the two lengths typically having their ends slightly overlapping. Each longitudinal section of the stripe laid down by the image-impressing device customarily has squared-off ends, the adjacent squared-off ends of adjacent stripe sections being disposed in slightly overlapping relationship with each other to provide the impression of a continuous stripe. For example, a typical prior art overlap was 0.0625-0.125 inch (1.6-3.1 mm). Assuming that the stripe section image on the image-impressing device is essentially a long, thin rectangle, if each impression is perfectly aligned longitudinally with respect to adjacent impressions, then an apparently continuous stripe of constant width and straight edges is formed, the apparently continuous stripe having a length greater than that of the image-impressing device.
However, if adjacent impressions are not perfectly aligned, a noticeable jog is created at the point where the end of the stripe section formed by one impression overlaps the end of the stripe section formed by the adjacent impression. Typically a noticeable jog is 1 to 2 mm (0.04 to 0.08 inch), depending on the width of the stripe. Since such jogs are commercially unacceptable, continuous stripes are usually printed by rotary printing methods.
To avoid or minimize such jogs, the printer typically relies on the use of a straight guide rail on the long table to insure that each impression is in longitudinal alignment with the adjacent impressions. For example, the frame of a silk screen may have two adjustable alignment screws longitudinally spaced along the side of the frame facing the rail. In making each impression, the printer places the screen on the long table with both screws in abutting contact with the guide rail. Thus the screws determine the alignment of the screen with respect to the guide rail against which the screws abut, and hence the screws and the guide rail together determine the alignment 9th screen in one position with respect to the screen when it is in upstream or downstream positions (i.e., used to form adjacent impressions).
Despite these mechanical aids, however, the possibility of imperfect alignment always remains. In hand printing, the printer may fail to place one or both of the screen's alignment screws in abutting contact with the guide rail. In both hand printing and flat-bed machine printing, the guide rails may deviate in places from a straight line by as much as a few millimeters. This deviation may result either from initial improper placement of the guide rail or from bending or warping of the guide rail over time. As the guide rail is typically formed of a number of different longitudinal sections in end-to-end relationship, such deviations typically occur at the joint or juncture between adjacent longitudinal sections of the rail. Any such deviation from linearity of the rail will typically result in a noticeable jog at the stripe section overlap of adjacent impressions if, on one impression, one adjusting screw of the screen touches the rail at one side of the rail section juncture and, on the adjacent impression, the other adjusting screw touches the rail at the other side of the juncture. The size of the resulting jog in the print is approximately equal to the size of the jog in the rail at the juncture between the misaligned rail sections.
Accordingly, it is an object of the present invention to provide a method of printing an apparently continuous stripe of constant width and straight edges without detectable jogs.
Another object is to provide such a method which produces an apparently continuous stripe with less apparent jogs.
A further object is to provide a substrate having an apparently continuous stripe thereon of constant width and straight edges made by such a method.